The invention herein is concerned with self-contained elevator constructions which are intended to find particular utility as means for providing access, particularly for personnel, to the platform of a drilling rig.
The use of elevators in this particular environment is known, note for example U.S. Pat. No. 3,592,294 to Allen. However, the known elevator systems have been found to be less than completely satisfactory for a variety of reasons. For example, in the above-noted patent, the elevator assembly is positioned at an inclined angle to the rig platform, thus requiring the use of substantial ground area adjacent the rig and necessitating the provision of means for adjusting the carrying cage so as to maintain a horizontal orientation thereof. In addition, the projection of the elevator assembly forms an obstruction into the surrounding work area. Another readily noted disadvantage is the inability of the patented elevator to provide access to intermediate points along the rig platform between the ground and deck levels.
Known examples of general purpose vertical elevator systems, in some instances incorporating hydraulic actuators in association with cables or chains, are set forth in the following U.S. Pat. Nos.:
220,040 Swartz; PA1 300,132 Rice; PA1 2,770,324 Peterson; PA1 3,003,584 Wiegand et al, PA1 3,207,263 Cull; PA1 3,360,078 Hopfeld; PA1 3,344,890 Loef; PA1 3,934,681 Herrell.
Such known elevator assemblies would find little utility in the particular environment of the invention due particularly to the construction and contemplated manner of operation as expressed in the various patents.